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    Subject[PATCH 4.14 42/71] ppp: unlock all_ppp_mutex before registering device
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Guillaume Nault <g.nault@alphalink.fr>


    [ Upstream commit 0171c41835591e9aa2e384b703ef9a6ae367c610 ]

    ppp_dev_uninit(), which is the .ndo_uninit() handler of PPP devices,
    needs to lock pn->all_ppp_mutex. Therefore we mustn't call
    register_netdevice() with pn->all_ppp_mutex already locked, or we'd
    deadlock in case register_netdevice() fails and calls .ndo_uninit().

    Fortunately, we can unlock pn->all_ppp_mutex before calling
    register_netdevice(). This lock protects pn->units_idr, which isn't
    used in the device registration process.

    However, keeping pn->all_ppp_mutex locked during device registration
    did ensure that no device in transient state would be published in
    pn->units_idr. In practice, unlocking it before calling
    register_netdevice() doesn't change this property: ppp_unit_register()
    is called with 'ppp_mutex' locked and all searches done in
    pn->units_idr hold this lock too.

    Fixes: 8cb775bc0a34 ("ppp: fix device unregistration upon netns deletion")
    Reported-and-tested-by: syzbot+367889b9c9e279219175@syzkaller.appspotmail.com
    Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/ppp/ppp_generic.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/drivers/net/ppp/ppp_generic.c
    +++ b/drivers/net/ppp/ppp_generic.c
    @@ -1003,17 +1003,18 @@ static int ppp_unit_register(struct ppp
    if (!ifname_is_set)
    snprintf(ppp->dev->name, IFNAMSIZ, "ppp%i", ppp->file.index);

    + mutex_unlock(&pn->all_ppp_mutex);
    +
    ret = register_netdevice(ppp->dev);
    if (ret < 0)
    goto err_unit;

    atomic_inc(&ppp_unit_count);

    - mutex_unlock(&pn->all_ppp_mutex);
    -
    return 0;

    err_unit:
    + mutex_lock(&pn->all_ppp_mutex);
    unit_put(&pn->units_idr, ppp->file.index);
    err:
    mutex_unlock(&pn->all_ppp_mutex);

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